This invention relates to a novel piston ring assembly for use in internal combustion engines or the like. More particularly, it relates to an oil ring assembly including a piston ring and an expansion ring.
Internal combustion engines, air compressors, and other piston equipment typically have compression rings and oil rings. The compression rings are usually circumferentially disposed around the piston end nearest the compression chamber. They form a gas tight seal between the piston and cylinder wall and provide a bearing surface to guide the piston as it reciprocates in the cylinder. The compression ring must accomplish these objectives reliably and be long lasting, despite the high temperatures and extremes in pressures encountered. Failure may lead to excessive wear, loss of power, a decline in efficiency, or scoring of the cylinder wall. Repair to correct these problems requires a major overhaul and down time of the engine.
The oil ring is usually located below the compression rings and in the piston ring grooves nearest the oil reservoir or source of cylinder wall lubrication. The purpose of an oil ring is to provide oil control and lubrication for the compression ring or rings by efficiently metering a very thin coat of lubricating oil onto the cylinder wall or cylinder liner wall over the entire stroke of the piston. While providing lubrication, the oil ring must also scrape excess oil from the cylinder wall and return it to the oil sump, thereby preventing such problems as fouling and excess oil consumption. The radially outward pressure of the oil ring against the cylinder wall is maintained primarily by an expansion ring, of either helical, serpentine, or similar configuration, which is interposed the piston and the oil ring and is circumferentially compressed when the piston ring is in the cylinder.
Oil control is further complicated because cylinder walls are not perfectly round. Hereinafter when referring to cylinder walls it is intended to include cylinder liner walls as well. Both old and new cylinders are subject to wear and fatigue and become distorted due to thermal, mechanical, or structural stress. Acordingly, piston rings must expand and contract along the entire length of the piston stroke to conform to the cylinder wall. This flexing is accommodated by the parted portion of the piston ring.
The constant flexing of the piston ring against the expansion ring often results in wear tracks being formed on the inner circumferential surface of the piston ring. This condition is normally enhanced at the parted portion of the oil ring, and as the expansion ring wears into the piston ring, the expansion ring becomes united with the piston ring and ceases to function independently as an expander. Continued flexing frequently causes the expansion ring to fracture in the vicinity where the piston ring is parted, thereby resulting in failure and requiring replacement thereof. To replace one or more rings involves substantial disassembly of the engine which is costly and time consuming.